1. Field of the Invention
The present invention relates to ferrite single crystals suitable for use in the manufacture of magnetic heads, particularly for video recording. The ferrites of the present invention contain lithium, iron, manganese, zinc, and optionally, cobalt.
2. Description of the Prior Art
Ferrite crystals composed of the Mn--Zn series have been used as suitable materials for magnetic heads. Such single crystals, however, are subject to processing deterioration due to magnetostriction and are likely to cause rubbing noises from the sliding contact between the magnetic tape and the magnetic head. In the case of video heads, such crystals are subject to mechanical distortion caused at the time of processing because of the shortening of tracks on video tapes, so that processing deterioration due to magnetostriction may cause a crucial problem.
Li--Zn series ferrite crystals, on the other hand, have been employed as magnetic head materials because they have a relatively low magnetostriction and have a high specific resistance, hardness and Curie point because of the absence of Fe.sup.2+ in the crystals, so that they have characteristics which the Mn--Zn series ferrite crystals do not have. The absence of the Fe.sup.2+ ions in the Li--Zn series single crystals, however, renders the equilibrium oxygen pressure high and such single crystals have such high melting points that it is difficult to grow single crystals from the molten state. Furthermore, ferrites of the Li--Zn series are likely to decompose at high temperatures and react with the material of the crucible, resulting in the evaporation of lithium, so that it is difficult to grow Li--Zn single crystals. The Li--Zn single crystals have heretofore been generally prepared by means of a fluxing method. This method involves melting raw materials constituting the Li--Zn series ferrite in a flux containing lead oxide and boric oxide, and allowing the Li--Zn series ferrite crystals to precipitate in the molten liquid by gradually cooling the liquid at a rate of about 2.degree. C. per hour. This fluxing method, however, presents disadvantages in that the flux may be contaminated in the precipitated crystals, the sizes of the single crystals are small, and the velocity of the crystal growth is slow.
An electromagnetic transducing head employed for video tape recorders has an extremely small size and may consist of a chip having a size, for example, of 2 mm in length, 3 mm in width, and 0.2 mm in thickness. An operating magnetic gap is formed on a portion of the chip which is brought into contact with the magnetic tape. The magnetic head chip has usually been constructed of a ferrite single crystal, having a magnetic gap depth, for example, of about 30 microns. In some cases, the magnetic head may be designed so that the single crystal constitutes both a surface abutting the tape and the operating gap, while other portions of the magnetic path may consist of a combination of the ferrite single crystal and ferrite polycrystals.
Video head chips in such small sizes may be manufactured by subjecting ferrite blocks to processing such as fusion for the formation of winding grooves or gaps and dividing the blocks into video head chips of a predetermined size.